The present invention relates to composite cables that include at least one optical transmission component and at least one electrical transmission component.
Fiber optic cables include at least one optical fiber that can transmit data, voice, and video information. Composite cable designs combine the high bit-rate capacity of at least one optical fiber with the electrical transmission of at least one electrical conductor. Conventional composite cable designs, however, can have unacceptable optical/electrical performance characteristics, can require undesirable structural features that make optical fiber access difficult, can be difficult to route through cable passageways, and/or can make the cable expensive to produce.
Conventional composite cables can include large and expensive electrical conductors. For example, U.S. Pat. No. 4,867,527, incorporated by reference herein, discloses a combined electrical power and optical fiber cable. The cable requires a large electrical conductor with insulation therearound, a sheath around the insulation, a one or two-part protective layer around the insulation, a tube within the protective layer, and at least one optical fiber loosely received in the tube. The protective layer can have armoring therearound and, in this case, the radial thickness of the protective layer is from two to four times the diameter of the tube.
A relatively large and expensive conventional composite cable has been designed for undersea applications. U.S. Pat. No. 5,468,913, incorporated by reference herein, discloses an electro-optical marine tow cable requiring a relatively large bundle of coaxial core conductors positioned at the neutral axis of the cable with the coaxial shield conductor circumscribing a dielectric material. The dielectric material includes fiber optic transmitters helically circumscribing the core conductors. Surrounding the electro-optical assembly is a watertight jacket and a protective armor cover for carrying the tensile forces imparted to the cable during marine towing operations.
A composite cable can include cable components that make optical fiber access difficult. For example, U.S. Pat. No. 5,202,944, requires an outer sheath made of stainless steel sheet having a thickness of 0.20 mm. The stainless steel sheet is formed into a tube shape and welded lengthwise to form the outer sheath. Coaxial cables can make fiber access difficult as they require multiple layers of electrical conductors, for example, as disclosed in U.S. Pat. No. 4,896,939 and U.S. Pat. No. 5,467,420.
One aspect of the present invention relates a compact composite cable that is operative to transmit in electrical and optical transmission modes. The composite cable includes an optical fiber operative to transmit light comprising a silica-based core with a silica-based cladding having a lower index of refraction than the core. The core and cladding are surrounded by at least one layer of plastic that defines a coating surrounding and in contact with the cladding, and has an outside diameter of about 250 xcexcm to about 500 xcexcm. An electrical conductor surrounds the coating, and the composite cable includes an outermost cable jacket layer having an outside diameter of about 3,500 xcexcm or less.